Plate tectonics, earthquakes and volcanoes

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Structure of the Earth

Earth has a layered structure: the crust (thin, rocky outer layer), the mantle (thick, hot layer of solid and flowing rock), and the core (made of iron and nickel).
The core is divided into a liquid outer core and a solid inner core.
The lithosphere is the rigid outer shell of Earth, including the crust and the uppermost part of the mantle.
The asthenosphere lies beneath the lithosphere; it is hotter and flows more easily, allowing the rigid plates above to move.
The lithosphere loses heat by conduction, while the asthenosphere also transfers heat by convection.

Tectonic Plates

The lithosphere is broken into large tectonic plates that fit together like a jigsaw.
There are seven or eight major plates (depending on how they are defined) and many minor plates or platelets.
Plates are made of oceanic crust (denser, thinner, lies below sea level) and/or continental crust (less dense, thicker, rises above sea level).
Plates move slowly over the asthenosphere, typically at speeds of 0 to 10 cm per year — about as fast as fingernails grow.
The theory of plate tectonics explains how these moving plates shape Earth's surface.

Convection Currents and Plate Movement

Convection currents in the mantle are the slow creeping motion of Earth's solid mantle, caused by lateral density variations.
At a seafloor spreading ridge, plates move apart and new crust forms; as it cools and moves away, it becomes denser, which helps drive motion.
At a subduction zone, cold, dense oceanic crust sinks into the mantle, forming the downward limb of a convection cell — this is the strongest driver of plate motion.
Other possible factors, such as active convection, upwelling inside the mantle, and tidal drag of the Moon, are still debated by scientists.

Plate Boundaries

Where plates meet, their relative motion determines the type of plate boundary (also called a fault).
Constructive (divergent) boundaries: plates move apart, and new crust forms by seafloor spreading.
Destructive (convergent) boundaries: plates move together, and one plate is forced down under the other in a process called subduction.
Conservative (transform) boundaries: plates slide past each other in opposite directions.
Faults at plate boundaries are geologically active, producing earthquakes, volcanic activity, mountain-building, and oceanic trenches.

How Earthquakes and Volcanoes Happen

Earthquakes occur when rocks at plate boundaries suddenly slip or break, releasing energy as seismic waves.
Volcanoes form where molten rock (magma) rises to the surface, often at constructive or destructive plate boundaries.
At destructive boundaries, subduction can create volcanoes and deep ocean trenches.
At constructive boundaries, magma rises to fill the gap as plates pull apart, forming new crust and underwater volcanoes.
At conservative boundaries, plates sliding past each other can cause earthquakes but usually no volcanoes.

Measuring Earthquakes

Earthquakes are measured using instruments called seismometers.
The Richter scale measures the magnitude (energy released) of an earthquake.
The Mercalli scale measures the intensity of shaking and damage caused by an earthquake.
Scientists also use the Moment Magnitude Scale (MMS) for larger earthquakes.
The focus is the point inside Earth where an earthquake starts; the epicentre is the point on the surface directly above it.

Effects of and Responses to Tectonic Hazards

Primary effects happen immediately, such as buildings collapsing, roads breaking, and people being injured or killed.
Secondary effects follow later, such as fires, landslides, tsunamis, disease outbreaks, and homelessness.
Responses include short-term actions (search and rescue, medical help, shelter) and long-term actions (rebuilding, strengthening building codes, education).
The impacts of a tectonic hazard are often more severe in a poorer country because of weaker buildings, fewer resources, and less preparedness.
A richer country can usually respond faster and recover more quickly due to better infrastructure, emergency services, and money.

Why People Live in Hazardous Places

People may live near volcanoes because the fertile volcanic soil is good for farming.
Geothermal energy from volcanic areas provides heat and electricity.
Tourism around volcanoes and earthquakes can create jobs and income.
People may have family ties, cultural connections, or simply cannot afford to move away.
Some people believe that the risk is low or that they can prepare for and manage the hazard.

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1.Which of the following sequences correctly lists the layers of the Earth from the surface inwards?
Easy
- ACrust, mantle, outer core, inner core
- BMantle, crust, inner core, outer core
- CCrust, outer core, mantle, inner core
- DInner core, outer core, mantle, crust
2.What is the name of the rigid outer shell of the Earth that is broken into tectonic plates?
Medium
- AAsthenosphere
- BLithosphere
- CMesosphere
- DOuter core
3.The theory of plate tectonics was widely accepted by scientists in the early 1900s.
Easy
True or false?
4.Which of the following are types of plate boundaries? (Select all that apply)
Medium
- AConstructive
- BDestructive
- CConservative
- DConvectional
- ETransform
5.Match the plate boundary type with its correct description.
Medium
- Constructive
- Destructive
- Conservative
- Plates move apart
- Plates move towards each other
- Plates slide past each other
6.Place the following events in the correct order to show how a destructive plate boundary can lead to an earthquake.
Medium
- Two plates move towards each other
- One plate is subducted beneath the other
- Friction causes the plates to stick
- Pressure builds up and is released as seismic waves
7.Which of the following best explains why tectonic plates move?
Medium
- AConvection currents in the mantle
- BThe gravitational pull of the Moon
- CEarth's magnetic field
- DThe rotation of the Earth
8.At which type of plate boundary are volcanoes most likely to form?
Medium
- AConstructive and destructive boundaries
- BConservative boundaries only
- CTransform boundaries only
- DConvection boundaries

Plus de questions

9.Match each layer of the Earth to its correct description.
Easy
- Crust
- Mantle
- Outer core
- Inner core
- Thin, rocky outer layer of the Earth
- Thick layer of hot, ductile rock between the crust and the core
- Liquid layer of metal surrounding the inner core
- Solid, extremely hot metal at the centre of the Earth
10.Which of the following are features or processes that occur at a divergent (constructive) plate boundary? (Select all that apply)
Medium
- ASeafloor spreading
- BFormation of new oceanic crust
- CSubduction of oceanic crust
- DMid-ocean ridges
- EDeep ocean trenches
11.Place the following events in the correct order to show how seafloor spreading creates new oceanic crust at a divergent plate boundary.
Medium
- Magma rises from the mantle
- New oceanic crust forms at the ridge
- The two plates move apart
- The new crust cools and moves away from the ridge
12.The asthenosphere is hotter and flows more easily than the lithosphere.
Easy
True or false?
13.Which of the following are ways that the movement of tectonic plates affects the Earth's surface? (Select all that apply)
Medium
- AEarthquakes
- BVolcanic activity
- CMountain building
- DOceanic trench formation
- EFormation of the Earth's magnetic field
14.Match each type of plate boundary to the correct description of how the plates move.
Medium
- Convergent (destructive) boundary
- Divergent (constructive) boundary
- Transform (conservative) boundary
- Plates move towards each other
- Plates move apart
- Plates slide past each other
15.Which statement best describes the relationship between the total surface area of the Earth's crust and plate tectonic processes?
Medium
- ASubduction reduces the surface area, while seafloor spreading creates new crust, so the total surface area stays roughly constant.
- BSeafloor spreading reduces the surface area, while subduction creates new crust, so the total surface area stays roughly constant.
- CBoth subduction and seafloor spreading add new crust, so the total surface area increases over time.
- DBoth subduction and seafloor spreading destroy crust, so the total surface area decreases over time.
16.Which of the following statements about the thickness of oceanic lithosphere are correct? (Select all that apply)
Medium
- AIt is thinnest at mid-ocean ridges.
- BIt becomes thicker as it moves away from the ridge.
- CIt is thickest at subduction zones.
- DIt remains the same thickness everywhere.
- EIt is thickest at mid-ocean ridges.
17.Place the following historical developments in the correct chronological order.
Medium
- The concept of continental drift is developed
- Seafloor spreading is validated
- Plate tectonics becomes widely accepted by geoscientists
18.What is the name of the supercontinent that began to break apart about 200 million years ago?
Easy
- APangaea
- BGondwana
- CLaurasia
- DRodinia
19.Approximately how fast do tectonic plates move per year?
Easy
- A0 to 10 cm
- B0 to 10 m
- C0 to 10 km
- D0 to 10 mm
20.At which type of plate boundary does subduction occur, leading to the formation of oceanic trenches and volcanic arcs?
Medium
- AConvergent boundary
- BDivergent boundary
- CTransform boundary
- DConservative boundary
21.Which of the following best explains why the total surface area of the Earth's crust remains constant over time?
Medium
- ANew crust is created at divergent boundaries while old crust is destroyed at convergent boundaries.
- BThe Earth's crust is constantly expanding due to seafloor spreading.
- CThe Earth's crust is shrinking because of subduction.
- DVolcanic eruptions add new crust without any crust being destroyed.
22.Which of the following are consequences of the movement of tectonic plates? (Select all that apply)
Medium
- AEarthquakes
- BVolcanic activity
- CMountain building
- DOceanic trench formation
- EFormation of hurricanes
23.A student writes: 'The idea of continental drift was developed in the first decades of the 20th century, and plate tectonics became accepted after seafloor spreading was validated in the mid- to late 1960s.' Which statement best describes the usefulness of this interpretation?
Medium
- AIt is useful because it correctly orders the development of the continental drift idea before the acceptance of plate tectonics.
- BIt is not useful because continental drift was developed after plate tectonics was accepted.
- CIt is not useful because seafloor spreading was validated in the 1800s.
- DIt is useful because it shows plate tectonics was accepted before continental drift was developed.
24.A data table shows the following plate speeds: Mid-Atlantic Ridge 10–40 mm/year; Nazca plate about 160 mm/year. What does this evidence suggest about plate motion?
Medium
- AAll plates move at exactly the same speed.
- BPlate speeds vary, with the Nazca plate moving much faster than plates at the Mid-Atlantic Ridge.
- CThe Mid-Atlantic Ridge is the fastest-moving plate boundary on Earth.
- DPlate motion only happens at the Nazca plate.
25.A short report states: 'Faults tend to be geologically active, with earthquakes, volcanic activity, mountain-building, and oceanic trench formation.' According to this evidence, which of the following are associated with active faults? (Select all that apply)
Medium
- AEarthquakes
- BVolcanic activity
- CMountain-building
- DOceanic trench formation
- EThe total surface area of Earth's crust increasing permanently
26.Evidence suggests that Jupiter's moon Europa shows signs of ice crustal plates moving and interacting, similar to Earth's plate tectonics.
Easy
True or false?
27.Match each statement about evidence for plate tectonics to the correct conclusion.
Medium
- Oceanic crust is denser than continental crust.
- New oceanic crust forms at divergent margins.
- Subduction carries one plate down into the mantle.
- Oceanic crust generally lies below sea level, while continental crust projects above it.
- This balances the crust lost at subduction zones, keeping total surface area constant.
- This reduces the total surface area of Earth's crust.
28.Place the following events in the correct order to show how the evidence for plate tectonics developed.
Medium
- The idea of continental drift is developed.
- Seafloor spreading is validated.
- Plate tectonics becomes widely accepted by geoscientists.
29.What does the data suggest about the relationship between distance from the ridge and thickness of oceanic lithosphere?
Medium
- AThickness decreases as distance from the ridge increases.
- BThickness increases as distance from the ridge increases.
- CThickness stays the same regardless of distance.
- DThickness is greatest at the ridge itself.
30.The data supports the idea that oceanic lithosphere cools and thickens as it moves away from the ridge.
Medium
True or false?
31.What is the name of the process by which one tectonic plate is forced down into the mantle beneath another plate?
Easy
- ASubduction
- BSeafloor spreading
- CConvection
- DContinental drift
32.Which of the following best describes the relative motion at a conservative (transform) plate boundary?
Medium
- APlates move towards each other
- BPlates move apart
- CPlates slide past each other
- DPlates move vertically
33.Which of the following is the correct order of the main layers of the Earth from the surface to the centre?
Medium
- ACrust, mantle, outer core, inner core
- BCrust, outer core, mantle, inner core
- CMantle, crust, outer core, inner core
- DCrust, inner core, outer core, mantle
34.Which of the following best explains why the total surface area of the Earth's crust remains roughly constant over time?
Medium
- ANew crust is formed at mid-ocean ridges at the same rate as old crust is destroyed at subduction zones
- BThe Earth is expanding, so new crust is added without any being destroyed
- CThe Earth is shrinking, so crust is destroyed faster than it is created
- DVolcanoes add new crust but it is immediately eroded away by rivers
35.Which of the following statements about the thickness of oceanic lithosphere is correct?
Medium
- AIt is thickest at mid-ocean ridges and thins towards subduction zones
- BIt is thinnest at mid-ocean ridges and thickens towards subduction zones
- CIt is the same thickness everywhere
- DIt is thickest in the middle of the ocean and thins towards the edges
36.A student writes: 'The idea of continental drift was developed in the first decades of the 20th century, and plate tectonics became accepted after seafloor spreading was validated in the mid- to late 1960s.' Which statement best evaluates this?
Medium
- AIt is correct: continental drift was an early 20th-century idea, and plate tectonics was accepted after seafloor spreading was validated in the 1960s
- BIt is incorrect: continental drift was developed in the 1960s, and plate tectonics was accepted in the early 1900s
- CIt is partially correct: continental drift was developed in the 1960s, but plate tectonics was accepted in the early 1900s
- DIt is incorrect: both ideas were developed in the 18th century
37.The lithosphere is cooler and more rigid than the asthenosphere.
Easy
True or false?
38.Oceanic crust is denser than continental crust.
Easy
True or false?
39.Match each type of crust or lithosphere to the correct description.
Medium
- Oceanic crust
- Continental crust
- Average oceanic lithosphere
- Continental lithosphere
- Denser, with less silicon and more heavy elements; forms at sea-floor spreading centres
- Thicker and buoyant; forms through arc volcanism and the accretion of terranes
- Typically about 100 km thick and varies with its age
- Typically about 200 km thick, though this varies between basins and mountain ranges
40.Which of the following statements about the lithosphere and asthenosphere are correct? (Select all that apply)
Medium
- AThe lithosphere loses heat mainly by conduction.
- BThe asthenosphere is cooler and more rigid than the lithosphere.
- CThe asthenosphere transfers heat by convection and has a nearly adiabatic temperature gradient.
- DThe division into lithosphere and asthenosphere is based on differences in mechanical properties and how heat is transferred.
- EA piece of mantle can be part of the lithosphere at one time and part of the asthenosphere at another, depending on temperature and pressure.
41.What is the name of the process where one tectonic plate is forced down into the mantle beneath another plate?
Medium
42.Approximately how many major tectonic plates are there on Earth?
Medium
43.Complete the sentence about the Earth's structure.
Easy
The Earth's outer layer is the ____, and beneath it lies the ____.
44.Complete the sentences about plate tectonics using the correct terms.
Easy
The process where one plate is forced down into the mantle beneath another plate is called ____. New oceanic crust is formed at divergent boundaries by ____. The rigid outer shell of the Earth that is broken into plates is the ____.
45.According to the reference material, what is the approximate maximum speed of the Nazca plate in millimetres per year?
Medium
46.Plate motions at the Mid-Atlantic Ridge range from 10 to 40 millimetres per year. What is the maximum speed of plate motion at the Mid-Atlantic Ridge, in millimetres per year?
Easy
47.Give the name of the plate that moves at about 160 millimetres per year, the fastest rate stated in the reference material.
Medium
48.Complete the sentence about the two types of crust using the correct terms.
Easy
Oceanic crust is denser than continental crust because it has less ____ and more of the heavier elements.
49.According to the reference material, what is the typical thickness of average oceanic lithosphere, in kilometres?
Easy
50.What is the name of the process by which new oceanic crust is formed at divergent margins, balancing the crust lost at subduction zones?
Medium
51.A map has a scale of 1:50,000. On the map, the distance between two points on a fault line is 6 cm. What is the real-world distance between these points, in kilometres?
Medium
52.Complete the sentence about the structure of the Earth using the correct terms.
Easy
The Earth's lithosphere is broken into seven or eight major ____ and many minor plates.
53.Explain why people continue to live in areas at risk from tectonic hazards.
Hard
54.Explain how convection currents in the mantle cause tectonic plates to move.
Hard
55.Explain how the evidence that oceanic lithosphere thickens with distance from a mid-ocean ridge supports the theory of seafloor spreading.
Hard
56.Approximately how many major tectonic plates are there on Earth?
Medium
- A8 plates
- B7 plates
- C6 plates
- D9 plates
57.According to the reference material, what is the approximate maximum speed of the Nazca plate in millimetres per year?
Medium
- A192 mm/year
- B176 mm/year
- C160 mm/year
- D144 mm/year
58.Plate motions at the Mid-Atlantic Ridge range from 10 to 40 millimetres per year. What is the maximum speed of plate motion at the Mid-Atlantic Ridge, in millimetres per year?
Easy
- A40 mm/year
- B36 mm/year
- C48 mm/year
- D44 mm/year
59.According to the reference material, what is the typical thickness of average oceanic lithosphere, in kilometres?
Easy
- A110 km
- B120 km
- C100 km
- D90 km
60.A map has a scale of 1:50,000. On the map, the distance between two points on a fault line is 6 cm. What is the real-world distance between these points, in kilometres?
Medium
- A5 km
- B3 km
- C2 km
- D4 km

Notes de révision

## Plate Tectonics, Earthquakes and Volcanoes ### Structure of the Earth - **Crust** – thin, rocky outer layer (oceanic or continental). - **Mantle** – thick layer below the crust; the upper part is the **asthenosphere**, which is hotter and flows more easily. - **Outer core** – liquid metal layer. - **Inner core** – solid metal centre. - The **lithosphere** is the rigid outer shell: the crust plus the upper mantle. It is broken into **tectonic plates**. ### Tectonic Plates - Earth's lithosphere is fractured into **seven or eight major plates** and many minor plates. - Plates are relatively rigid and **float across the ductile asthenosphere**. - They move because of **convection currents** – the slow creeping motion of Earth's solid mantle caused by lateral density variations. - Plates move **0 to 10 cm per year** (10–40 mm/year at the Mid-Atlantic Ridge; up to about 160 mm/year for the Nazca plate). - **Oceanic crust** is denser than **continental crust** because it has less silicon and more heavier elements. Oceanic crust lies below sea level; continental crust projects above it. ### Plate Boundaries Where plates meet, their relative motion determines the boundary type: - **Convergent (destructive)** – plates move towards each other. **Subduction** carries the edge of one plate down under the other into the mantle. This reduces Earth's surface area and forms oceanic trenches, earthquakes and volcanoes. - **Divergent (constructive)** – plates move apart. New oceanic crust forms by **seafloor spreading** at mid-ocean ridges, balancing the crust lost at subduction zones. - **Transform (conservative)** – plates slide past each other. Faults are geologically active, causing earthquakes. ### Earthquakes and Volcanoes - Most earthquakes and volcanoes occur at **plate boundaries**, where faults are active. - **Earthquakes** happen when plates suddenly slip along faults, releasing energy. - **Volcanoes** form where magma rises to the surface, especially at divergent boundaries and subduction zones. - Earthquakes are measured using the **Richter scale** (magnitude). ### Hazards: Rich vs Poor Countries - **Richer countries** can afford better building codes, prediction technology, emergency services and rapid responses, reducing deaths. - **Poorer countries** often have weaker buildings, less planning and slower responses, so more people die and damage is greater. ### Why People Live in Hazardous Places - Fertile volcanic soils, geothermal energy, tourism, jobs, family ties, and belief that an eruption or earthquake will not happen in their lifetime. ### Key Idea Plate tectonics is the scientific theory that Earth's lithosphere comprises a number of large tectonic plates which have been slowly moving since 3–4 billion years ago.

Lithosphere: The rigid outer shell of the planet, including the crust and upper mantle.
Asthenosphere: The hotter, ductile part of the upper mantle beneath the lithosphere; it flows more easily and plates ride on it.
Tectonic plate: A large, relatively rigid slab of lithosphere that moves over the asthenosphere.
Convection currents: The slow creeping motion of Earth's solid mantle caused by lateral density variations; they drive plate movement.
Convergent boundary: A plate boundary where plates move towards each other; subduction occurs, forming trenches, earthquakes and volcanoes.
Divergent boundary: A plate boundary where plates move apart; new oceanic crust forms by seafloor spreading at mid-ocean ridges.
Transform boundary: A plate boundary where plates slide past each other; faults are active and earthquakes occur.
Subduction: The process along convergent boundaries where the edge of one plate is carried down under another plate into the mantle.
Seafloor spreading: The formation of new oceanic crust along divergent margins, balancing crust lost at subduction zones.
Oceanic crust: Denser crust formed at seafloor spreading centres; it lies below sea level.
Continental crust: Less dense crust formed through arc volcanism and accretion; it projects above sea level.
Fault: A fracture between plates where they meet; geologically active with earthquakes, volcanic activity and mountain-building.
Richter scale: A scale used to measure the magnitude of earthquakes.

Cartes mémo

What is the theory of plate tectonics?

The scientific theory that Earth's lithosphere is broken into large tectonic plates that have been slowly moving for 3–4 billion years.

What is the lithosphere?

The rigid outer shell of Earth, including the crust and the uppermost mantle.

What is the asthenosphere?

The hotter, ductile layer beneath the lithosphere on which tectonic plates move.

Name the four main layers of Earth's structure.

Crust, mantle, outer core, and inner core.

What are tectonic plates?

Large, rigid slabs of lithosphere that float on the asthenosphere and move slowly.

What drives the movement of tectonic plates?

Convection currents in the mantle, caused by lateral density variations and heat transfer.

What is a constructive plate boundary?

A boundary where plates move apart (divergent), allowing magma to rise and new crust to form.

What is a destructive plate boundary?

A boundary where plates move towards each other (convergent), often causing subduction.

What is a conservative plate boundary?

A boundary where plates slide past each other (transform), without creating or destroying crust.

What is subduction?

The process where one tectonic plate is forced down into the mantle beneath another plate at a convergent boundary.

How do earthquakes occur at plate boundaries?

When plates suddenly slip past each other, releasing stored energy as seismic waves.

How do volcanoes form at plate boundaries?

Magma rises from the mantle through weaknesses in the crust, often at constructive or destructive boundaries.

What is the Richter scale used for?

Measuring the magnitude (energy released) of an earthquake.

What is the Mercalli scale used for?

Measuring the intensity of an earthquake based on observed effects and damage.

Give one effect of an earthquake in a richer country.

Buildings may be damaged, but well-enforced building codes and emergency services can reduce deaths.

Give one effect of an earthquake in a poorer country.

Buildings may collapse more easily, leading to higher casualties and slower recovery due to limited resources.

Why do people live in hazardous places?

For fertile volcanic soils, geothermal energy, tourism, jobs, or because they have always lived there.

What is the difference between oceanic and continental crust?

Oceanic crust is denser and thinner, while continental crust is less dense and thicker.

What is seafloor spreading?

The process where new oceanic crust forms at mid-ocean ridges and spreads outwards.

What is a fault?

A fracture in Earth's crust where rocks on either side have moved past each other.

How fast do tectonic plates move?

Typically from 0 to 10 cm per year, about as fast as fingernails grow.

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